The present invention has been developed as a metal forming operation with particular applicability to the making of head suspensions for the disk drive industry. Head suspensions, to which the present invention is directed, comprise components made of spring metal for supporting magnetic read/write heads within certain disk drive assemblies. These head suspensions are typically very small in size and comprise many features related to its ability to very accurately but compliantly position a read/write head over a data track of a disk within the disk drive assembly. With the trend to increase density of such disks and to utilize even smaller disk drives, head suspensions must also be made smaller, but must also still include many tiny features to ensure accurate operation. Head suspensions are typically made from stainless steel sheet material having thicknesses ranging of between 0.05 mm and 0.10 mm.
Metal forming, as required in the field of making head suspensions, typically includes operations such as stamping, bending, cutting, or otherwise shaping sheet stainless steel material. Usually, such metal forming operations are performed on blanks of the material that have been previously cut or shaped from a sheet of the material, such as by a chemical etching process. Preferably, the blanks are made attached to a carrier strip so that any number of forming operations can be conducted by moving the carrier strip with its attached blanks throughout the requisite number of forming stations.
More specifically, a station performs a forming operation on every blank (unless, possibly, if it is rejected) that is moved through that station in sequence. Then, a next forming operation, and further for as many as are required, are performed by additional machines. The need for additional machines to perform each step of the manufacturing process, including a variety of metal forming steps, requires significant floor space within such a manufacturing facility. Moreover, in order to minimize rejected parts and to maximize feature accuracy, metal forming equipment typically includes significant structure for alignment of the forming components.
Forming practice typically includes a four-post die set utilizing roller ball bearings having cages to guide and align the top and bottom die sets. One of the die sets is normally actuated by pneumatic, hydraulic or mechanical means while the other die set remains stationary within the machine. This type of construction requires the provision of pressure pads, various springs and complex tooling to achieve the needed motion and clamping within the die set. With the use of machines of this type, many tolerances are included within the tool guiding and actuation systems that build on top of one another and can negatively affect the accuracy of die alignment and thus the forming operation. This stack-up of tolerances may render this type of machine unacceptable where very precise forming operations are required.
One development for increasing accuracy and speed in a metal forming operation is disclosed in a U.S. Pat. No. 4,866,976 to Hinterlechner. In the Hinterlechner apparatus, accuracy is achieved by reducing stack-up tolerances in guiding a punch and die set. Specifically, a reference plane is very accurately defined so that a punch and die are accurately guided over the reference plane with respect to one another on at least that one level. Moreover, a roller bearing guide structure is defined wherein the bearings are preloaded to further enhance the accuracy of movement of each of the punch and die. The punch and die are simultaneously moved toward one another by a mechanical drive mechanism. In addition to minimizing stack-up tolerances which can lead to a larger chance of punch and die misalignment, the use of roller or needle bearings is advantageous in that they can handle many times higher loading rates and stiffness as compared to ball bearing cages. Such ball cages have a much greater tendency to deform when placed under heavy loads as compared to roller bearing cages because of the point contact that the balls make instead of the line contact of roller bearings.